From what I understand, it's the anti-predation chemicals, particularly in the skin which can be toxic, or at least gut irritating to humans.

Maybe sweet potatoes don't have the same chemical defenses as regular potatoes, but it seems reasonable to think they have some mechanism not to be consumed by mold, fungi, etc. Otherwise, they would be extinct.

OMG you just demanded me of the roasted potato man! I lived in Japan for a while, and at night this haunting song would come through the windows....hiya YAAAAkiiiii IMO......it was like a rolling hot dog cart only it sold roasted yams. so so good after a few beers. Ah, those were the days

It seems to me that tubers growing in the ground need to defend themselves somehow. If now from toxins in the skin, then how? Maybe it's a moot point if you don't eat the skin, as long as the toxins are not on the inside. So, it sounds like potato toxins are more of a problem for some people than others.

I agree. :( I love sweet potatoes, but yet when you look at the kitavans they are fine. Did they adapt to convert better? Is avoidance of PUFAs and making sure your thyroid is in optimal condition key to consuming large quantities of beta carotene? I don't know.

Mark Sisson agrees with you there (see my post below). Is there a way to verify this? I have seen data (somewhere...) that the antinutrients are mostly in the skin for potatoes, but how can we know it's also true for sweet potatoes?

Yams and yucca basically have bark around them -- not really edible at all! I suppose sweet potato skin is edible, but I do not eat it. I believe that most of the antinutrients to be found, if any, are going to be found in the skin.

interesting! so what do you think about the need to peel the skin off of yams and sweet potatoes versus regular ole taters, yay or nay? (I have no idea what a Yucca/cassava is, so i'm not gonna worry about that for now...)

Yup, yams are in dioscoreaceae. I don't have info if yams are any more or less safe than sweet potatoes. They are nearly pure starch, so they fit into the same good use cases that sweet potatoes do -- really great after some exercise. Yucca/cassava, on the other hand, has a good amount of saponins in it, that requires precooking and removing the center of the root.

so I get that yams and sweet potatoes are different. but does that matter for these purposes? Is a yam better/worse to consume than a sweet potato? Do I need to skin either/both before i make awesome fries?

P.S. One of my favorite pedantic points, but sweet potatoes are **not** yams. Yams are something completely different - much more starchy, and somewhat like a cassava, potato, and chestnut combined in flavor.

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The difference lies in the specific antinutrients. There are a few in nightshades, and a few in sweet potatoes, but the nightshade ones have more obvious effects (at least regarding pain). See tab two in this article I wrote a couple months ago:

As you can see, the interaction of nightshades with acetylcholine degredation and possibly production is a major culprit. The vitamin D angle...interesting but not entirely convincing to me. When they find evidence of soft tissue calcification with nightshade consumption, I'll be more convinced.

I have never, anecdotally, heard of someone having acute rheumatological distress from sweet potatoes. But tummy upset? Oh yes! I don't react well to having too many sweet potatoes or weird Asian/African tubers. Maybe it's partly psychosomatic. Who knows.

Sweet potatoes are not nightshades. All nightshades are in the solanaceae family and sweet potatoes are in the convolvulaceae family.

Tubers are tubers, sure. But all plants have evolved with various chemical defenses; we don't always attempt to eat the portions that contain these chemicals, so that works out usually. There are some plants, like peppers, whose chemical defenses we actually seek out (i.e. the capsacin in hot peppers only mammals can taste, but birds cannot -- encouraged the pepper seeds to be distributed widely, and not crowdedly).

So, no plant is completely free from chemical defenses. If you find that you tolerate sweet potatoes well, like many can, then rest assured that eating one is likely more healthy than harmful.

so I get that yams and sweet potatoes are different. but does that matter for these purposes? Is a yam better/worse to consume than a sweet potato? Do I need to skin either/both before i make awesome fries?

Mark Sisson agrees with you there (see my post below). Is there a way to verify this? I have seen data (somewhere...) that the antinutrients are mostly in the skin for potatoes, but how can we know it's also true for sweet potatoes?

interesting! so what do you think about the need to peel the skin off of yams and sweet potatoes versus regular ole taters, yay or nay? (I have no idea what a Yucca/cassava is, so i'm not gonna worry about that for now...)

Yup, yams are in dioscoreaceae. I don't have info if yams are any more or less safe than sweet potatoes. They are nearly pure starch, so they fit into the same good use cases that sweet potatoes do -- really great after some exercise. Yucca/cassava, on the other hand, has a good amount of saponins in it, that requires precooking and removing the center of the root.

Yams and yucca basically have bark around them -- not really edible at all! I suppose sweet potato skin is edible, but I do not eat it. I believe that most of the antinutrients to be found, if any, are going to be found in the skin.

It seems to me that tubers growing in the ground need to defend themselves somehow. If now from toxins in the skin, then how? Maybe it's a moot point if you don't eat the skin, as long as the toxins are not on the inside. So, it sounds like potato toxins are more of a problem for some people than others.

Wonder if sweet potatoes aren't safe because of the large quantities of beta carotene?

Are Carotenes Safe?
Are carotenes safe in large doses, as claimed? Dependence on carotenes for vitamin A calls on large reserves of enzymes to make the conversion. In their fascinating book Nutrition and Evolution, Michael Crawford and David Marsh note that in animals, "if any function can be delegated to another organism it leaves the disk space free to perform some new function or to perform an old one better." The cat species does not synthesize vitamin A from carotenes. "If they had to synthesize their own vitamin A . . . it would take up a significant amount of their disk space." Cats get vitamin A from their prey, whose ability to synthesize vitamin A from carotenes compromises other functions, such as night vision and quickness of movement. While medical orthodoxy claims that consumption of large amounts of carotenes has no downside, it is possible that dependence on carotenes for vitamin A, even in those who are good converters, compromises other biochemical functions in subtle ways.

The so-called nontoxic betacarotene supplements contain a synthetic form of carotene, just one of 50 or 60 carotenes found in the typical diet. The biological activity of synthetic betacarotene is much lower than that of the natural complexes of carotenes and, in fact, may put stress on the immune system Studies with humans and rats given synthetic betacarotene found an increase in white blood cells. In cancer trials, synthetic betacarotenes were not found to be protective. In fact, in one study, patients given synthetic betacarotene had worse results than controls (NEJM April 1994 330:(15);891-895).

I agree. :( I love sweet potatoes, but yet when you look at the kitavans they are fine. Did they adapt to convert better? Is avoidance of PUFAs and making sure your thyroid is in optimal condition key to consuming large quantities of beta carotene? I don't know.

This awesome article by Mark Sisson answers most of my questions about yams and sweet potatoes, it's pretty comprehensive. Though this part is disappointing, i mean can't we find this out for sure!?:

"Traditionally, sweet potato and yam skins are removed before consumption, so I err on the side of caution and do the same. I doubt a bit of skin is going to hurt you, though, if you decide to eat it. Most of the anti-nutrients in potatoes can be found in the skin, and it seems logical to assume the same is true for yams and sweet potatoes."

From what I have heard on various Robb Wolf podcasts sweet potatoes are okay but should be pealed if you have an autoimmune disease or serious gut sensitivity. Nearly everything has some degree of antinutrients but it's all about quantity and type.